Method for assembling a pelton turbine wheel

ABSTRACT

The invention concerns a method which consists in: pre-positioning, in a housing ( 7 ) of a flange ( 5 ), a bucket ( 2 ) supported by part ( 23 ) of its outer surface ( 23 ) against an edge ( 71 ) of the housing ( 7 ) providing a space (E′) between the convex surface ( 23 B) of the outer radial part ( 2 B) of the bucket ( 2 ) and said edge ( 71 ); producing an articulated linkage ( 15 ) of the bucket ( 2 ) on the rim ( 1 ) and/or the flange ( 5 ) on the inside ( 2 A) of the bucket ( 2 ); exerting on the outer radial part ( 2 B) of the bucket ( 2 ) a first calibrated force to bring it closer to the edge ( 71 ); determining the distance (e) between said outer radial part ( 2 B) and said edge ( 71 ) under said force; slackening said force; arranging, between said outer radial part ( 2 B) and said edge ( 71 ), a wedge ( 53 ) having a thickness substantially equal to said distance (e); and exerting on the outer radial part ( 2 B) of the bucket a second force (F 2 ) to bringing it closer to the edge and maintaining said second force (F 2 ) which has an intensity not less than that of the first force.

The invention relates to a method for assembling a Pelton turbine wheel,to a bucket for such a wheel and to a wheel equipped with such a bucket.

Pelton turbines are conventionally used for transforming the kineticenergy of a fluid, such as the water of a waterfall, into mechanicalenergy. Such transformation is effected by rotating the turbine wheelunder the effect of a tangential force exerted, on buckets arranged onthe periphery of a rim, by a jet of water emerging from one or moreinjectors distributed around the wheel.

International Patent Application WO-A-99/49213 discloses using twoannular flanges fast with the rim for supporting the buckets of a Peltonturbine wheel, which allows an optimalized distribution of the forcesundergone by the buckets, the mechanical stresses in that case no longerbeing concentrated in a zone of fastening of the bucket on the rim. Inthis known device, each bucket is in abutment, by a convex surface,against radial arms of the flanges and immobilized with respect to eachflange thanks to a locking screw.

The buckets of such a turbine wheel undergo a large number of impactsdue to the jets of driving fluid coming from the injectors. The effectof these impacts is to apply each bucket alternately on the radial armsagainst which it is in abutment, which results in an alternate stressingof the materials constituting the buckets and the flanges. In addition,the surface abutment of the buckets on the flanges necessitates aprecise adjustment of the outer dimensions of each bucket and of thecorresponding housings provided in the flanges. Such an adjustment doesnot allow interchangeability of the buckets, which accordingly rendersmanufacture and maintenance of such a wheel complex.

It is a more particular object of the invention to overcome thesedrawbacks by proposing a method for assembling a wheel, as known fromWO-A-99/49213, which makes it possible to avoid that the impacts of thejets of driving fluid generate alternate fatigue and/or stressing of thebucket with respect to the rim or to the flanges.

This method consists in:

pre-positioning, in a housing of a flange, a bucket supported by a partof its outer convex surface against an edge of this housing, providing aspace between the convex surface of the outer radial part of this bucketand this edge;

producing an articulated linkage of this bucket on the rim and/or theflange on the inside of the bucket;

exerting on the outer radial part of the bucket a first calibrated forceto bring it closer to the flange;

determining the distance between this outer radial part and this edgeunder this calibrated force;

slackening this calibrated force;

arranging, between this outer radial part and this edge, a wedge havinga thickness substantially equal to the distance mentioned above, and

exerting on this outer radial part and maintaining a second force tobring it closer to the edge, this second force having an intensitygreater than or equal to that of the first force.

Thanks to the invention, the bucket mounted on the wheel is subjected toa pre-stress formed by the second calibrated force which has the effectof immobilizing it firmly with respect to the flange and ofcompensating, with the wedge, the spacing existing between the outerradial part of the bucket and the flange. After establishment of thepre-stress, the wedge makes it possible to “filter” the dynamic forcesexerted on the bucket, particularly at the level of its outer radialpart. The use of a wedge, of thickness determined as a function of theexact geometry of the bucket and of the flange and of the reaction ofthe bucket to the first calibrated force of bringing closer, makes itpossible to envisage an interchangeability of the buckets, only thethickness of each wedge having to be adjusted precisely to the geometryof the surrounding parts.

According to a first advantageous aspect of the invention, the methodconsists in exerting the calibrated forces by means of a locking screwreceived in a housing made in the flange and penetrating in a tappingmade in the outer radial part of the bucket. The calibrated force maythus be exerted by means of a torque wrench or any other controlledtightening means and have a considerable intensity, particularly in thecase of a wheel of large diameter.

According to another advantageous aspect of the invention, theafore-mentioned first and second calibrated forces for bringing closerare substantially of the same intensity. Thus, when the wheel is inmounted configuration, each bucket is in abutment against thecorresponding wedge under the effect of the calibrated force used fordetermining the thickness of this wedge. This assembly makes it possibleto obtain a constant force in the locking screws by filtering thealternate forces due to the impacts of the jets of fluid.

The invention also relates to a turbine wheel bucket carrying out themethod as described hereinbefore and, more specifically, to a bucketcomprising a bi-concave surface for flow of a fluid for driving thewheel and a convex surface adapted to cooperate with at least oneannular flange fast with a rim of the wheel. This bucket ischaracterized in that its convex surface forms at least one abutmentzone located against the flange and at least one zone distant from theflange in an outer radial part of the bucket, this zone distant from theflange being adapted to be brought closer to a part of the flangelocated opposite by a calibrated force.

According to advantageous but non-obligatory aspects of the invention,this bucket incorporates one or more of the following characteristics:

The convex surface of the bucket also forms a zone distant from theflange in an inner radial part of the bucket. Thus, the localizedabutment zone on the face is formed solely in a central part of thisconvex surface, which allows a certain displacement of the bucket in aradial direction.

The bucket comprises, at the level of the outer radial part and/or theinner radial part of its concave surface, at least one guide adapted togive to the flow of the afore-mentioned fluid a divergent componentwhich is accentuated with respect to a median edge of the bucket. Thisguide makes it possible to avoid the fluid in the course of flowstriking a radial arm of the flange disposed opposite the concavesurface of the bucket. This guide may be provided to be adapted todirect the flow up to the level of a recess made in a radial arm of theflange disposed opposite this concave surface. This guide isadvantageously formed by a rib extending, from an outer radial end zoneof the bucket, in the direction of an inner radial part of the bucket,this rib bordering the outer notch of the bucket.

Finally, the invention relates to a Pelton turbine wheel which comprisesa rim, at least one annular flange, fast with the rim and provided withhousings for receiving buckets, and at least one bucket as describedhereinbefore.

Such a wheel advantageously comprises, for this bucket or for eachbucket, a wedge disposed between the afore-mentioned distant zone andthe flange, the bucket or each of the buckets being subjected to acalibrated force of bringing this distant zone and the flange closer.

According to another advantageous aspect of the invention, the or eachflange is provided with recesses for flow of the fluid driving theturbine from the concave surface of each bucket, the recesses beingformed on an outer lateral surface of the flange.

The invention will be more readily understood and other advantagesthereof will appear more clearly in the light of the followingdescription of two embodiments of a Pelton turbine wheel in accordancewith its principle, given solely by way of example and made withreference to the accompanying drawings, in which:

FIG. 1 is a view in partial perspective of a Pelton turbine wheelaccording to the invention.

FIG. 2 is a section along line II—II in FIG. 1.

FIG. 3 is a section along line III—III in FIG. 2 during a first step ofassembly of the wheel of FIG. 1, a plurality of buckets being shown.

FIG. 4 is a view similar to FIG. 3 during a second step of the method ofassembly.

FIG. 5 is a view similar to FIG. 3 during a third step of the method ofassembly.

FIG. 6 is a view in partial perspective of the bucket of the wheel ofFIGS. 1 to 5.

FIG. 7 is a view similar to FIG. 6 for a bucket according to a secondembodiment of the invention.

The turbine wheel shown in FIGS. 1 to 6 comprises a rim I and buckets 2,eighteen in number in the example shown, distributed on the periphery ofthe rim 1. Each bucket comprises two ladles or bowls 3 separated by amedian edge 4 intended to be arranged opposite one or more water orvapour injectors (not shown). The rim 1 is provided to be mounted on ashaft for transferring the movement (likewise not shown).

In order to render the drawing clearer, only one bucket has been shownin FIG. 1.

Two ring-shaped flanges 5 and 6 are mounted on the rim 1 and contributeto holding the buckets 2 with respect to this rim. The flanges 5 and 6are respectively provided with housings 7 and 8 in which the bowls 3 ofthe buckets 2 may be inserted. Two bands 9 and 10 of continuous matterare respectively formed in the outer peripheral zones of the flanges 5and 6. These bands 9 and 10 join radial arms 11 and 12 formed by theflanges 5 and 6, respectively between adjacent housings 7 and 8.

Each bucket 2 is mounted on the rim 1 and the flanges 2 thanks to a pin15 installed as a so-called “compound” assembly and appearing moreclearly in FIG. 2. This pin comprises a slightly conical principal body15A inserted in a split sleeve 15B, itself introduced in correspondingbores in flanges 5 and 6 and the rim 1. A locking screw 15C cooperateswith a washer 15D for tightening the pin 15 in position.

Each bucket 2 defines two concave surfaces 21 and 22 between whichextends the edge 4 along a radial axis X-X′ forming axis of symmetry ofthe bucket 2. The bucket 2 also defines two convex surfaces 23 and 24together forming the outer surface of each bowl 3. Each bucket 2comprises an inner radial part 2A at the level of which it is connectedwith the rim 1 and the flanges 5 and 6 by the pin 15. Each bucket 2 alsocomprises an outer radial part 2B located in the vicinity of the bands 9and 10 when the wheel is in mounted configuration and in which there isdefined an outer notch 25 allowing the injection of the jet of water inthe bucket 2.

23A and 23B respectively denote the inner and outer radial parts of thesurface 23.

As is more clearly visible in FIGS. 3 to 5, a heel or projecting part23C projects beyond the surface 23 with respect to parts 23A and 23B,the heel 23C being formed in an intermediate zone of the bucket 2.

The geometry of the surface 24 is similar to that of the surface 23 andalso comprises a projecting part or heel.

Each housing 7 is defined by a concave edge 71 and a substantiallyrectilinear edge 72 between which is inserted a bowl 3 of a bucket 2,the surface 23 of this bowl going alongside the edge 71. Similarly, eachhousing 8 receives the bowl 3 of the bucket 2 located on the left ofaxis X-X′ in FIG. 2.

As is more particularly visible in FIG. 3, the geometry of the edge 71and of the surface 23 is such that the surface 23 is in abutment againstthe edge 71 solely at the level of its central zone or heel 23C, twospaces E and E′ being respectively formed between the part 23A and theedge 71, on the one hand, and between the part 23B and the edge 71 onthe other hand.

During the step of assembly of the wheel shown in FIG. 3, each bucket 2is positioned in the corresponding housings 7 and 8 and the pin 15 isinserted in the corresponding bores of the buckets of the rim and theflanges, without tightening this pin, so that an articulated linkage isproduced of each bucket on the rim and the flanges.

There is then inserted in a housing 51 provided in the band 9 of theflange 5, a screw 52 whose shank traverses the housing 51 and may beinserted in a tapping 23D provided in the part 23B of the surface 23.The screw 52 is then screwed with a torque wrench or other controlledtightening means such as a pre-stress jack or a heating pipe, so as toobtain a calibrated force for bringing closer the part 2B of the bucket2 and the edge 71 of the housing 7. One proceeds in the same wayconcerning the second bowl of the bucket 2.

One is then in the position of FIG. 4 where a calibrated force F₁ isexerted on the part 2B by the screw 52 and the equivalent screw providedin the second flange 6. In this configuration, the distance e existingbetween the part 23B of the surface 23 and the edge 71 of the housing 7is measured. This distance e may be different from one bucket to theother taking into account the manufacturing tolerances of the rim, theflanges and the buckets. The equivalent distance between the outer partof the surface 24 and the concave edge of the housing 8 is measured.

In practice, all the buckets 2 are positioned in the housings 7 and 8and all the screws 52 and equivalent are progressively tightened inlogical order, in order to place all the buckets under pre-stress F₁ forbringing closer their respective outer radial parts 2B with respect tothe flanges 5 and 6 in order to ensure an overall symmetry. Thedistances e are then measured, as these distances depend in particularon the distribution of forces in the flanges 5 and 6.

When the distances e have been determined, wedges 53 are fashioned, ofwhich each has a thickness equal to the distance e between a bucket andthe flange as defined hereinbefore. Then, after having loosened thescrews 52, i.e. released the force F₁, each of the wedges 53 ispositioned between the bucket 2 and the edge 71 or equivalent of thehousing 7 or 8 in which it is inserted and for which the wedge 53 hasbeen fashioned. In other words, each wedge 53 is intended for a coupleformed by a bucket 2 and a housing 7 or 8.

When the wedge 53 is in place, the screws 52 and equivalent aretightened again, with a calibrated force F₂ of intensity greater than orequal to that of the force F₁ used previously. The outer radial part 2Bof each bucket 2 is thus subjected to a force F₂ for bringing closerthis part with respect to the edge 71 or equivalent of the housing.

As the force F₂ is at least as intense as the force F₁, one is sure thatthe part 23B of the surface 23 is in firm abutment against the wedge 53which is itself in firm abutment against the edge 71 of the housing 7 orequivalent. Each bucket is thus subjected to a pre-stress F₂ whichapplies it efficiently against the flange, in pivoting about the axis ofthe pin 15. Each bucket 2 is therefore firmly maintained in position anddoes not risk oscillating under the effect of the impacts of the fluidissuing from the injectors.

The pins 15 are then tightened so that the articulated linkage createdat their level is locked.

At the end of assembly, the bucket 2 may be modelized like a beamarticulated towards the pin and in abutment on the central zones 23 cand equivalent while it is subjected to a force of application againstthe edge 71.

As is more particularly visible in FIG. 5, each bucket 2 is subjected toa force of reaction R by the flange 5 or 6 and to the force F₂, theforce F₂ having an intensity equal to the section of the screw 52multiplied by the force of tightening.

In the case of a screw of type M16 tightened to 200 MPa, the force F₂has a value defined as follows:

F ₂=144 mm ²×200 MPa=28 800 N

The tangential component F′₂ of the force F₂ is equal to F′₂=F₂×cos (α)where α is the angle of the force F₂ with respect to the reaction R.Assuming α to be equal to 30°, one obtains:

F′ ₂=24 940 N.

At equilibrium, the pre-stress exerted by the force of reaction R on thebucket 2 which results from the component F′₂ may be expressed as afunction of the distances d₁ and d₂ defined respectively between the pin15 and a point of application of the reaction R and between the pin 15and the point of application of the force F₂ such that

R=F′ ₂×d₂/d₁.

Furthermore, the force of the impact exerted by the jet on each bucket 2may be determined by calculation and it suffices to choose the force oftightening of the screws 52 and equivalent and the ratio d₂/d₁ for theforce R to be permanently greater than or equal to the force undergoneby the bucket under the effect of the impact mentioned above. A safetycoefficient of the order of 1.5 may, for example, be used.

Thus, each bucket is firmly maintained in position with respect to itsenvironment and the material constituting it is not stressed in fatigueby the impacts that it undergoes.

The method of the invention is efficient as long as the force F₂ isgreater in value than the force F₁, which makes it possible to ensurethat each bucket 2 is effectively applied against the adjacent wedge 53or equivalent.

According to an advantageous variant of the invention, the forces F₁ andF₂ may be substantially equal, in which case the screws 52 andequivalent are not subjected to a high elongation force while eachbucket is efficiently maintained in position.

The fact that a space E is provided between the part 23A of the surface23 and the edge 71 ensures that the system formed by a bucket 2 and aflange 5 or 6 is isostatic.

As is more particularly visible in FIGS. 2 and 6, the outer radial parts21B and 22B of the concave surfaces 21 and 22 are each provided with arib 21C or 22C adjacent the notch 25. The function of these ribs is todeviate the flow of water represented by arrow F₃ in FIG. 2 towards theoutside of the space E″ defined between the flanges 5 and 6.

In order to avoid the flow of water deviated by the ribs 21C and 22Cstriking the rectilinear edges 72 and equivalent of the housings 7 and8, these edges are provided, on the outer faces 5A and 6A of the flanges5 and 6, with recesses, 73 for the edges of housings 7 and 83 for theedges of housings 8. Thanks to these recesses 73 and 83, the flow ofwater F₃ may be evacuated without generating a force of braking of thewheel which might occur if the water flowing over the surfaces 21 and 22struck the edges 72 and equivalent of the housings 7 and 8.

As is more particularly visible in FIG. 6, the rib 21 c has a depth anda thickness which decrease on moving away from the edge 21D of thesurface 21.

As shown in FIG. 7, the function of the rib 21 c may also be obtained bya concave zone 121C provided in the outer radial part 121B of theconcave surface 121 of a bucket in accordance with a second embodiment.

Towards the inner part 21A or 22A of the surfaces 21 and 22, the latterare provided with a lining 21E or 22E making it possible also to divertthe flow F₃ towards the outside of the flanges 5 and 6, withoutinterference with the rectilinear edges of the housings 7 and 8.

As before, recesses 74 and 84 may be provided on the flanges 5 and 6, atthe level of the edges of the housings 7 and 8, to avoid an interferencebetween the flow F₃ and these edges. In a variant, the linings 21E and22E extend up to outside the flanges 7 and 8, with the result that it isnot necessary to provide recesses in the inner parts of the arms 11 and12.

The invention has been described with a turbine wheel comprising a rimand two flanges added on this rim. It is also applicable to the case ofthe rim being formed by two half-rims each integrating an annular partforming flange, as described in the second embodiment of WO-A-99/49213and, more generally, to any turbine wheel comprising a rim and at leastone flange.

What is claimed is:
 1. Method for assembling a turbine wheel of Peltontype comprising a rim (1), a plurality of buckets (2) distributed overthe periphery of this rim and at least one annular flange (5, 6) fastwith said rim and provided with housings (7, 8) for receiving saidbuckets, characterized in that it consists in: pre-positioning, in ahousing (7) of said flange, a bucket (2) supported by a part (23C) ofits outer convex surface (23) against an edge (71) of said housing,providing a space (E′) between the convex surface (23B) of the outerradial part (2B) of said bucket and said edge (71); producing anarticulated linkage of said bucket (2) on the rim and/or said flange (5)on the inside (2A) of said bucket; exerting on said outer radial part(2B) of said bucket a first calibrated force (F₁) to bring it closer tosaid flange; determining the distance (e) between this outer radial part(2B) and this edge (71) under said force (F₁); slackening said force(F₁); arranging, between said outer radial part (2B) and said edge (71),a wedge (53) having a thickness substantially equal to said distance(e), and exerting on said outer radial part (2B), and maintaining asecond force (F₂) to bring it closer to said edge (71), said secondforce (F₂) having an intensity greater than or equal to that of saidfirst force (F₁).
 2. Method according to claim 1, characterized in thatit consists in exerting said calibrated forces (F₁, F₂) by means of alocking screw (52) received in a housing (51) made in said flange (5, 6)and penetrating in a tapping (23D) made in the outer radial part (2B) ofsaid bucket (2).
 3. Method according to claim 1, characterized in thatsaid first and second calibrated forces (F₁, F₂) for bringing closer aresubstantially of the same intensity.
 4. Pelton turbine wheel bucketcomprising a bi-concave surface (21, 22) for flow (F₃) of a fluid fordriving said wheel and a convex surface (23, 24) adapted to cooperatewith at least one annular flange (5, 6) fast with a rim (1) of saidwheel, characterized in that said convex surface (23) forms at least oneabutment zone (23C) located against said flange (5, 6) and at least onezone (23B) distant from said flange in an outer radial part (2B) of saidbucket (2), said zone (23B) distant from said flange being adapted to bebrought closer to a part of the flange located opposite, by a calibratedforce (F₁, F₂).
 5. Bucket according to claim 4, characterized in thatsaid convex surface (23, 24) forms a zone (23A) distant from said flange(5, 6) in a radial part (2A) inside said bucket (2).
 6. Bucket accordingto claim 4, characterized in that it comprises, at the level of theouter radial part (21B,22B) and/or the inner radial part (21A, 22A) ofits concave surface (21,22), at least one guide (21C,22C,2lE,22E)adapted to give the flow (F₃) of said fluid a divergent componentaccentuated with respect to the median edge 94) of said bucket (2). 7.Bucket according to claim 6, characterized in that said guide (21C, 22C,21E, 22E) is adapted to direct said flow (F₃) up to the level of arecess (73, 74, 83, 84) made in a radial arm (11, 12) of said flange (5,6) disposed opposite said concave surface (21, 22).
 8. Bucket accordingto claim 7, characterized in that said guide is formed by a rib(21C,22C) extending, from an outer radial end zone (2B) of said bucket(2), in the direction of an inner radial part (2A) of said bucket, thisrib bordering an outer notch (25) of said bucket.
 9. Pelton turbinewheel comprising a rim (1) and at least one annular flange (5,6) fastwith said rim and provided with housings (7,8) for receiving buckets,characterized in that it comprises at least one bucket (2) according toclaim
 4. 10. Turbine wheel according to claim 9, characterized in thatit comprises, for said bucket (2) or each of said buckets, a wedge (53)disposed between said distant zone (23B) and said flange (5, 6), saidbucket or each of said buckets being subjected to a calibrated force(F₂) for bringing said distant zone and said flange closer.
 11. Turbinewheel according to claim 10, characterized in that said or each flange(5,6) is provided with recesses (73,74,83,84) for flow of the fluiddriving the turbine from the concave surface (21,22) of each bucket (2),said recesses being formed on an outer lateral surface (5A,6A) of saidflange (5,6).